The load on an electric fence energiser can be quite variable according to a number of factors such as the moisture content of the ground, leakage at fence posts and of course the electrical resistance that occurs when an animal comes in contact with the fence. So as to detect whether an animal has come in contact with the fence it is necessary for energisers to periodically send out electrical pulses.
Most electric fence energisers can only provide a single output pulse which is fed to the fence regardless of the load. The pulse needs to be sufficiently powerful to deter an animal in contact with the fence, however, it is wasteful if the fence load is light. With an energiser operating above fence load requirements as in the above situation the life of the energiser is often unnecessarily reduced.
Direct measurement of the load on a transformer within the energiser is difficult as a number of countries have safety regulations that require 10 000 volts isolation between the primary and secondary coils and transformers.
Efforts have been made to address the above problem and electric fence energisers that have varied pulses are known. For instance, U.S. Pat. No. 2,981,854 discloses an energiser that continuously and alternately charges the fence with high and low voltage surges. This however does not have a means of monitoring the actual fence load and therefore cannot selectively respond according to the load.
U.S. Pat. No. 3,378,694 does monitor load requirements but the monitoring means is not from within the energiser but via a "feeler" which determines the conductivity of the soil into which the feeler is placed. This provides an unrepresentative value depending on the location of the feeler and does not test directly the load to which the energiser itself is operating under.
Another problem associated with electric fence energisers is that they are responsible for radio interference by the nature of their operation and in countries that rely heavily upon radio communication a reduction of the source of interference would be welcomed.
It is an object of the present invention to provide an electric fence energiser that addresses the above problems.
Further objects and advantages of the present invention will become apparent from the ensuing description which is given by way of example.